udp checksum implementation error in FreeBSD 7.2?

[Benoit Panizzon]

Hi

We are running a DHCP Server on a FreeBSD 7.2-RELEASE-p4 box.

This works for most of our customers, except ones with some kind of SonicWall 
Firewalls. We have analyzed the problem with the sonicwall tech support:

We found the problem being in the sonicwall setting a UDP checksum of 0x0000 
for DHCP Requests.

According to the RFC this is a valid value and tells the receiving UDP stack 
not to check the checksum:

http://www.faqs.org/rfcs/rfc768.html

If the value is different from 0x0000 the receiving UDP stack can perform a 
checksum check and if this fails, silently drop that packet.

What we observe is:

DHCP Request with UDP checksum set => Packet reaches DHCP Daemon and is being 
answered.
DHCP Request with UDP checksum 0x0000 => ICMP Port Unreachable from FreeBSD.

Can someone confirm this non RFC conform behaviour and knows how to fix it?

As I understand, setting net.inet.udp.checksum to zero would not fix the 
problem, as this is only for packet generation.

Kind regards

Benoit Panizzon
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